A rotational phase difference-adjusting device varies a rotational phase difference of a camshaft relative to a crankshaft in an internal combustion engine for adjusting operating timing of an engine valve. The rotational phase difference-adjusting device is provided with a variable valve timing mechanism and an oil control valve. The variable valve timing mechanism is usually provided with rotational elements connected respectively to the crankshaft and the camshaft. An advance chamber for advancing a rotational angle of the camshaft and a retard chamber for retarding it are defined in the two rotational elements. The oil control valve is an electromagnetic driven type valve which supplies oil to one of the advance chamber and the retard chamber and discharges it from the other.
On the other hand, a control device for controlling the rotational phase difference, at the time of holding the rotational phase difference, operates the oil control valve to prevent inflow and outflow of oil between the advance chamber and the retard chamber. In addition, at the time of variably controlling the rotational phase difference to a desired value, the control device operates the oil control valve to adjust an inflow amount of the oil to one of the advance chamber and the retard chamber and an outflow amount of the oil from the other.
The variable control for the rotational phase difference actually sets as a reference a holding learning value as an operational signal of the oil control valve which can hold the rotational phase difference and is performed by operating the oil control valve with a feedback correction amount based upon a difference between an actual rotational phase difference and a target value. However, the operational signal which can hold the rotational phase difference changes with a rotational speed of the crankshaft, temperatures of oil or the like. This change invites deterioration in controllability of the feedback control.
Conventionally, there is, as shown in JP-8-74530A (U.S. Pat. No. 5,562,071), proposed a control device which in advance sets the holding learning value for each region of plural regions regionally divided based upon a rotational speed of a crank shaft and temperatures of oil. According to this technology, even if a learning value capable of holding the rotational phase difference in response to the rotational speed or the temperature of the oil changes, an appropriate holding learning value can be used, resulting in maintaining high controllability of the rotational phase difference.
In this case, however, since the holding learning value is required for each region, a great deal of work is to be required for adaptation of the holding learning value.
In view of the above, there exists a need for a control device for an engine valve and a control system for an engine valve which overcome the above mentioned problems in the conventional art. The present invention addresses this need in the conventional art as well as other needs, which will become apparent to those skilled in the art from this disclosure.